The Everett woman was making a Valentine’s Day card, and knew just how it should look. With patience and dexterity, Hoover helped make it so, applying glue to the snippet of a smile.

“I really enjoy this,” said Hoover, an Archbishop Murphy High School student who joined other teens volunteering Monday at Full Life Care. The nonprofit organization, once known as ElderHealth Northwest, provides seniors and others with adult day health care programs.

Wearing United Way “Live United” T-shirts, nearly 20 young people helped at the Everett facility as part of the Martin Luther King Jr. Day of Service. This is the fourth year United Way of Snohomish County has joined in the national day of service, conceived as a “day on” for volunteers, rather than a day off.

Almost 300 volunteers pitched in at MLK Day of Service sites around the county, including 250 teens, according to Neil Parekh, spokesman for the local United Way.

Along with the helpers at Full Life Care, volunteers helped seniors and people with disabilities with household chores in Marysville, Mukilteo, Sultan and Everett, and served at senior centers in Stanwood, Arlington, Mountlake Terrace and Lynnwood.

Members of Lynnwood’s Girl Scout Troop 40283 joined Archbishop Murphy High School students for Monday’s valentine-making and a volleyball game at Full Life Care.

Derry Henrick, activity coordinator at Full Life Care, said morning sessions serve people with chronic illnesses and brain injuries. Clients in an afternoon group are adults with developmental disabilities.

For Monday’s volleyball game, players sat in rows — with Beach Boys classics as accompaniment — and used fists and foam-noodle water toys to hit balloons over the net.

“We do physical and cognitive exercise every day,” Henrick said. Funding comes from Medicaid and private insurance, said Moe Pocha, program manager at Full Life Care. “This keeps people moving and engaged in life,” Pocha said. “For a lot of clients, this is the only place they get out to. Some really wonderful friendships are born here.”

Lynnwood High School ninth-graders Anika Hildebrand, Natalie Brown and Arielle Effenberger were quick to make friends with several women at the center.

“They have some interesting stories to tell,” said Effenberger, a 15-year-old member of the Girl Scout troop. “One lady told us her boyfriend had back surgery. She told us, ‘Now I know how it feels to be one of you young girls, missing a boyfriend,’ ” said Brown, whose mother, Wendy Brown, was there as troop leader.

Hildebrand sees progress in the evolution of the King holiday message. From its focus on equality, the day is also now about serving others. “We learned about Martin Luther King Jr. in elementary school,” said Hildebrand, who added that her generation didn’t experience the racial divide of King’s era. “We grew up in a diverse society,” she said. “This is helping the community.”

Hoover wasn’t the only teen boy making valentines.

“It was kind of hard getting up this morning, but I love this. It’s fun,” said Chris Wilson, 14, an Archbishop Murphy freshman. He and classmate Kyle Malone, 15, were helping Julie Montgomery make cards.

Montgomery, 52, suffers from heart trouble. She comes to the center four days a week. The exercise, social interaction, healthful meals and help she gets at Full Life Care make a big difference to her.

“I’m so much better since I came here,” said Montgomery, who was making a valentine for her father. Chatting with her teen helpers, she said, “You’re only 15, and you want to be here with us.”

Montgomery is old enough to have memories of King’s mission, and of the world he helped change.

“That was a wonderful man,” she said. “The day of giving really should be every day.”